Viscosity

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Hi,
Just learning how to read oil product information.
Question about viscosity at 40 and 100, is better to have them lower or higher number?
Different brands have different lower and upper index.
Thanks
 
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Better for what?

And if you’re “just learning” then stick to the grade designation. If you don’t understand that then you’re not going to understand the rest.
 
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Question about viscosity at 40 and 100, is better to have them lower or higher number?
In a nutshell simplistic explanation ... a lower viscosity at 40C would give better/easier cold starts if you're in a cold winter climate, and a higher viscosity at 100C would give better engine protection. So if you wanted good cold weather starting, and at the same time good hot engine protection if you're pushing the engine hard, you'd go for a 0W-30 or 0W-40 instead of a 5W-20 as an example.

40C and 100C is the temperature of the oil of course ... just to be sure you get that part.
 

free2d

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So simply put it the most ideal is the widest range possible between them, lowest 40 and highest 100 index you can find at a certain oil index xWxx.
Thanks again.
 
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In a nutshell simplistic explanation ... a lower viscosity at 40C would give better/easier cold starts if you're in a cold winter climate, and a higher viscosity at 100C would give better engine protection. So if you wanted good cold weather starting, and at the same time good hot engine protection if you're pushing the engine hard, you'd go for a 0W-30 or 0W-40 instead of a 5W-20 as an example.

40C and 100C is the temperature of the oil of course ... just to be sure you get that part.
Sorry but Dude, you smoking something tonight? 40C easier starting? That's got almost nothing to do with starting thickness, it's 104F. OP would be better served to see the viscosity chart for low temperature requirements for labeling. Can't do it myself due to limitations on phone.

OP, start out choosing an oil recommended for your vehicle. Oil temps at 40C will be reached and passed as your engine warms up, and at operating temperature of ~100C it will be within the range specified for that viscosity.

Or, interpreting your post differently, the debate on this site -- as to whether thicker or thinner oil is better -- is an epic and continuing one. Some prefer a thicker oil for a stronger film strength since it's a layer of oil that separates moving metal parts. Some prefer thinner to increase flow rate, choosing to rely on additives to protect the engine if the boundary layer goes away. Additives have improved greatly in the last several years, which fuels the discussion.

Both schools of thought have their merits, and as stated before the ongoing debate between the schools of thought has been, and likely will continue to be, epic. There's no single easy answer - millions of vehicles using 20 grade oils (of all variance of thickness within the grade) have not had engine failures. Conversely, many manufacturers recommend a 20 grade oil but state in the owner's manual something to the effect that a thicker oil is required under certain conditions. Plus, Ford has gone back to a 30 for their truck V8 engines from their earlier recommendation of a 20.

Recommended reading: CAFE

edit: ZeeOSix, I see free2d's interpretation of your post now, and if that is what you intended I apologize for jumping all over your post earlier in this one.
 
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free2d

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Sorry if I cause any discomfort.

I am looking at 5W40 grade oil for my old Honda Accord 2005. Nothing fancy.

After searching thru different brands such as Amsoil, LiquiMoly, Castrol etc. I started to notice, learn and understand, there is more questions of whys/hows.

For the [email protected], I understand lower is better.

As for [email protected], well I don’t know, higher or lower is better? Lower so that at 100C will flow better all over the engine and not “heavy”? Or higher at high temperature so it holds viscosity.

Thank you.
 
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Sorry but Dude, you smoking something tonight? 40C easier starting? That's got almost nothing to do with starting thickness, it's 104F. OP would be better served to see the viscosity chart for low temperature requirements for labeling. Can't do it myself due to limitations on phone.

edit: ZeeOSix, I see free2d's interpretation of your post now, and if that is what you intended I apologize for jumping all over your post earlier in this one.
You might want to try grasping the words a bit better before starting off a reply like that ... 😂 I was talking about comparing different viscosities to each other in a simplied matter. Oils with a lower KV40 will also be thinner at lower temps than oil with a higher KV40. and therefore will provide better cold starting in cold conditions. And oils with a higher KV100 will provide better protection when the oil is at 200+ F. It's a well know fact of tribology that thicker viscosity provides more MOFT which gives more protection from moving parts contacting each other and causing metal-on-metal wear. You've been here since 2005 and should have read that about 1000 times over the years.

If "oil A" has a lower viscosity at 40C then "oil B", then "oil A" is also going to have a lower viscosity at temperatures below 40C. Don't let 40C hang you up. Speaking of the viscosity vs temperature chart, go use Widman's viscosity vs temperature calculator and look at the plot curves of different oil's using their KV40 and KV100 data points and you'll see what I mean.

Anyway ... apology accepted. ;)
 
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As for [email protected], well I don’t know, higher or lower is better? Lower so that at 100C will flow better all over the engine and not “heavy”? Or higher at high temperature so it holds viscosity.
All viscosity oils will flow well at 100C (212F) when the oil is at full operating temperature. However, a 40 weight is going to give more oil film thickness between moving parts than a thinner oil at 100C, and help better prevent any metal-to-metal contact and wear.
 
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Or, interpreting your post differently, the debate on this site -- as to whether thicker or thinner oil is better -- is an epic and continuing one. Some prefer a thicker oil for a stronger film strength since it's a layer of oil that separates moving metal parts. Some prefer thinner to increase flow rate, choosing to rely on additives to protect the engine if the boundary layer goes away. Additives have improved greatly in the last several years, which fuels the discussion.
There is a difference between oil "film strength" and oil "film thickness". Sounds like you're talking about MOFT ... Ie, film thickness, not film strength. And yes, they are both important.

Read this Machinery Lubrication article: https://www.machinerylubrication.com/Read/30835/lubricant-film-strength

I believe in obtaining protection from wear with the viscosity by counting on it preventing metal-to-metal contact (ie, higher MOFT). Film strength is only the 2nd level of defense AFTER the metal-to-metal contact has already occurred.

Both schools of thought have their merits, and as stated before the ongoing debate between the schools of thought has been, and likely will continue to be, epic. There's no single easy answer - millions of vehicles using 20 grade oils (of all variance of thickness within the grade) have not had engine failures.
Engines can have more wear over the long run from using thinner oils, and never have an "engine failure". Those two things are way far apart from each other. As they say, most people don't keep vehicles forever, so what the hay if they wear out a bit more from thinner oil use while they own them, lol.

Conversely, many manufacturers recommend a 20 grade oil but state in the owner's manual something to the effect that a thicker oil is required under certain conditions. Plus, Ford has gone back to a 30 for their truck V8 engines from their earlier recommendation of a 20.
Yes, and hence why I like relying on viscosity as the first line of defense to protect the engine. The AW/AF additives that provide the "film strength" can then kick in IF the viscosity doesn't prevent the metal-to-metal contact between moving part.
 
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free2d

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Manual stated 5W30, 5W40, 10W30.
Using 5W30 now, thinking oil change to 5W40 since old car.
 
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You might want to try grasping the words a bit better before starting off a reply like that ... 😂 I was talking about comparing different viscosities to each other in a simplied matter. Oils with a lower KV40 will also be thinner at lower temps than oil with a higher KV40. and therefore will provide better cold starting in cold conditions. And oils with a higher KV100 will provide better protection when the oil is at 200+ F. It's a well know fact of tribology that thicker viscosity provides more MOFT which gives more protection from moving parts contacting each other and causing metal-on-metal wear. You've been here since 2005 and should have read that about 1000 times over the years.

Don't let 40C hang you up. Speaking of the viscosity vs temperature chart, go use Widman's viscosity vs temperature calculator and look at the plot curves of different oil's using their KV40 and KV100 data points and you'll see what I mean.

Anyway ... apology accepted. ;)

I have read it more than 1000 times, no need to be condescending. You and I are in agreement on oil thickness.

I've used the Widman calculator numerous times. Perhaps our definition of "cold start" is different. I was simply (and indirectly) pointing out that a 40C/104F start is very different than a -30C/-22F start, and that since OP had questions that a chart might have been more helpful to illustrate your point.

Parsing each comment I made takes them out of context, so please, in your words, try grasping the meaning in a holistic sense and not breaking posts up into bits prior to commenting.

;)
 
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There wouldn’t be any issues even if the owners manual didn’t “allow” (recommend) it. There is no conceivable instance where at 40-grade would damage his engine.
Obviously, but given the noobness of the situation, if the manual says 5W-40 is fine, then it just backs up the fact that it won't "hurt" anything.
 
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I have read it more than 1000 times, no need to be condescending. You and I are in agreement on oil thickness.

I've used the Widman calculator numerous times. Perhaps our definition of "cold start" is different. I was simply (and indirectly) pointing out that a 40C/104F start is very different than a -30C/-22F start, and that since OP had questions that a chart might have been more helpful to illustrate your point.
I wasn't trying to define the definition of "cold start". All I was saying (and you can verify it with the viscosity calculator), is that if "Oil A" is thinner at 40C than "Oil B", then "Oil A" also going to also be thinner at any temperature below 40C and therefore be better for cold starting. I was trying to put it in simple terms that someone without much grasp of viscosity vs temperature seems to have, and all he's looking at is viscosity numbers of different oils at 40C and 100C.

OP could also look at the CCS (Cold Cranking Simulator) and Pour Point temperature numbers (if available) for a feel of the really cold viscosity for starting on super cold mornings, if that something he's doing.
 
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